1. Field of the Invention
The present invention relates to a mobile communication system, and more particularly a method and an apparatus for adjusting a power in a communication system.
2. Discussion of the Related Art
Generally, a 1x cdma2000 system is designed to support a voice service of a circuit switched mode and a medium and low-speed data service. Also, as the desire for a mobile Internet service and so on increases, a system only for a high-speed packet data communication, to the exclusion of the voice service, has been proposed, which is called a high data rate (HDR) or an 1x-evolution data only (1x-EV DO).
A combined version of the two systems is called a 1x-evolution data and voice (1x EV DV).
The 1x-EV DV system is a system that can perform the voice service and data service of the existing circuit mode simultaneously with a high-speed packet data service.
Accordingly, the 1x-EV DV system should be compatible with 1x of the existing cdma2000 system in a lower direction. Thus, all the currently considered 1x-EV DV standards support a radio configuration (RC) of the existing cdma2000 system, and have independent RC type shared channels for a packet data service in addition.
Basically, the shared channel (hereinafter, referred to as a forward packet data channel (F-PDCH)) for the packet data service can accommodate many users by using a time division multiplexing (TDM) like the HDR or using a mixed type of a code division multiplexing and the TDM.
The 1x-EV DV system uses a method of dynamically allocating an extra base station power and Walsh code to the F-PDCH in a state that voice users and data users of the existing circuit mode exist. Also, the 1x-EV DV system increases the data throughput of the base station by using a method of allocating the extra base station power and the Walsh code to a specified user having a good-quality link. At this time, for the operation of the F-PDCH is required a certain feedback channel for the respective user's transmission of the link quality between the user and the base station to the base station.
The base station performs a scheduling of the target users to whom the data is to be transmitted at the present time based on the link quality reported by the users, and selects a modulation technique and a channel coding rate suitable for the present link quality to transmits the modulation technique and the channel coding rate to the scheduled target users.
Also, in order to improve the data throughput, the F-PDCH operates a hybrid-automatic repeat request (H-ARQ) on a physical layer. For such an operation of the H-ARQ is required a reverse feedback channel for the terminal's judgment of existence/non-existence of an error in a received packet and transmission of an acknowledgement (ACK) or non-acknowledgement (NACK) bit to the base station.
The reverse feedback channel for transmitting the link quality is called a reverse channel quality indication channel (R-CQICH), and the reverse feedback channel for transmitting the ACK or NACK bit is called a reverse acknowledgement channel (R-ACKCH).
In order for the base station to properly receive the reverse feedback channels, it can be considered that a power control with respect to the reverse channels is a required process.
Basically, an IS-2000 system generates a power control bit (PCB) for a forward link power increasing or decreasing command by measuring a dedicated pilot power level of the respective terminal transmitted in a reverse direction, transmits the PCB for each power control group (PCG) by carrying the PCB on traffic information of a forward fundamental channel (F-FCH) or a forward dedicated control channel (F-DCCH), and performs the reverse power control of 800 Hz accordingly.
However, in the 1x-EV DV system, the F-FCH or F-DCCH is not always allocated to the active users (i.e., users having links set for receiving the data from a transmitting end) who will receive the packet data.
Accordingly, a certain new channel is required for the reverse power control, and the channel used for this purpose is just a forward common power control channel (F-CPCCH).
FIG. 1 is a view illustrating the construction of the conventional F-CPCCH channel.
As shown in FIG. 1, blocks for a forward common power control channel are symbol repeat blocks 102 and 109, signal point mapping blocks 103 and 110, channel gain sections 104 and 111, multiplexers 101 and 108, a relative offset calculation section 105, a decimator 106, and a long code generator 107.
The multiplexers 101 and 108 receive the power control bits (PCBs) through branches I and Q, and multiplex the PCBs by users. At this time, the multiplexers 101 and 108 adjust offset values of the PCBs by users according to the offset values provided from a relative offset calculation section 105.
The symbol repeat blocks 102 and 109 do not repeat the multiplexed PCBs through the branch I or Q in case that a transmission (Tx) diversity mode is not used, while they repeat the multiplexed PCBs only once in case that the Tx diversity mode is used.
The signal point mapping blocks 103 and 110 perform the mapping of ‘0’ onto ‘+1’, ‘1’ onto ‘−1’, and ‘0’ in case that no transmission bit exists among the PCBs. The channel gain sections 104 and 111 adjust the channel gain to be used for the transmission in the unit of a power control group. The long code generator 107 generates a long code according to a long code mask for the power control channel, and the decimator 106 detects the long code in the unit of a chip, and provides the detected long code to the relative offset calculation section 105. Accordingly, the relative offset calculation section 105 calculates the offset values by users, and provides the offset values to the multiplexers 101 and 108.
In FIG. 1, if it is assumed that the F-CPCCH channel performs the reverse power control for 800 Hz, the power control bits (PCBs) for 24 active users are transmitted in one power control group (PCG). At this time, the PCBs for the 12 users are allocated to the branch I, and the PCBs for the remaining 12 users are allocated to the branch Q. Also, a process of randomizing positions of the PCB bits in one PCG by users through a relative offset calculation is performed. Also, if it is assumed that the F-CPCCH channel performs the reverse power control for 400 Hz and 200 Hz, the PCBs for the 48 users and the 96 users can be accommodated in one F-CPCCH channel, respectively.
The F-CPCCH channel is a common channel, and it is required that the users far apart from the base station can receive the channel with reliability. That is, the power control for the reverse feedback channels can be performed with reliability only in case that the F-CPCCH can accurately judge the PCB bits allocated to the F-CPCCH itself The simplest usable method is a method of performing the transmission with a sufficiently high power so that the users located on the edge of the cell can receive the PCB bits with a sufficient reliability.
This method has the following problem. Since PCBs for the user located far away from the base station may be included on the F-CPCCH, the base station should allocate to the F-CPCCH a high power sufficient for the user to receive its own PCB. At this time, the forward packet data channel (F-PDCH) uses all the remaining power of the base station for the packet transmission. However, if the F-CPCCH is transmitted always with a high power, the transmission power for the F-PDCH would be lost, and this causes the reduction of the data throughput of the forward link.
Accordingly, in order to solve this problem, the forward power control should be performed in the unit of a bit with respect to the respective users who belong to one power control group.